Endogenous Opioid Regulation of Gonadotropin-Releasing Hormone Release from the Human Fetal Hypothalamusin Vitro*

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Abstract
Endogenous opioid regulation of GnRH release from the human fetal (21–23 weeks gestation) mediobasal hypothalamus was investigated in an in vitro perifusion system. Pulse injection of an opiate receptor antagonist, naloxone, reproducibly elicited an acute increase in GnRH release within 30 min. Constant infusion of naloxone (60 min) induced a sustained increase in GnRH release, which was promptly inhibited by a pulse of β-endorphin administered halfway during the naloxone infusion. These studies unequivocally demonstrate that endogenous opiates exert an inhibitory effect on GnRH release from the human fetal mediobasal hypothalamus in vitro.